And he said the wider international community had to step up and contribute to humanitarian efforts which are currently substantially short of the funds required.

A citizen journalism image of Syrians paying their respect to those killed in Damascus

Updating the House on the situation in Syria as MPs gathered for the first day of the new session, Mr Hague said more than 20,000 people had died in the fighting over the past 17 months, 1.5 million are internally displaced, and 230,000 have fled across borders to Lebanon, Iraq, Turkey and Jordan.

The foreign secretary said: "On three occasions we have tried with our partners to adopt a Security Council resolution that would require the regime to begin a political transition, rather than simply call on it to do so.

"On each occasion, Russia and China have used vetoes, most recently on 19 July.

"It is a terrible indictment of the Council that approximately a quarter of all those who have been killed in Syria died in the month following the last vetoed resolution.

"We continue to urge Russia and China to work with us to end the crisis and to allow the Security Council to live up to its responsibilities."

Mr Hague told MPs the government was working in five areas in a bid to support the Syrian people in the absence of a coherent international response.

He said they were helping to create the conditions for a political transition, providing further humanitarian aid, increasing the pressure on the regime, supporting justice for victims of human rights violations and planning assistance to a future Syrian government.

Actions are being co-ordinated with allies but the funding required to deliver the humanitarian aid needed is not in place.

"As of last week, the 180 million dollar UN Humanitarian Response Plan was only half funded," Mr Hague said.

"There is an urgent need for other countries to help make up the shortfall."

In response, shadow foreign secretary Douglas Alexander endorsed the government's strategy for dealing with the situation.

He said: "Since the last time we debated the situation, the pace of the conflict unfolding in Syria has quickened and the situation on the ground worsened.

"Do you accept the situation in Syria continues to represent not only, of course, a terrible indictment of Assad's brutality but also a tragic failure by the international community?

"The longer the conflict continues, the greater the risk of a rise in jihadism on the one hand, and of indiscriminate sectarian violence on the other, making a sustainable resolution to the conflict even harder to achieve.

"Do you accept there is today not an agreed legal basis or indeed public appetite for British ground-based forces to be deployed in Syria?

"It is imperative therefore the government focuses its efforts in the weeks ahead in unifying the international community's response, uniting a fractured opposition behind a credible plan for an inclusive political transition, and addressing the continued and on-going humanitarian need of the millions suffering in Syria today.

"If that is the focus of work in the weeks ahead, you will continue to have opposition support."

Mr Hague replied: "I agree about what you said about the deployment of British ground forces, this is not something I've heard anybody advocate in this country, but it is also true we do not know how this will develop in the coming months.